I use this PowerPoint for my 8th grade Science class. The PowerPoint covers the two types of changes; physical and chemical. The difference between reactants and products is explained. The types of chemical reactions such as synthesis and decomposition are explained. The rest of the slides involve the law of conservation of mass, balancing chemical equations, exothermic and endothermic reactions, photosynthesis vs. respiration, and solutes vs. solvents.